In vitro diagnostics (IVD) allows labs to assist in the diagnosis of disease based on assays performed on patient fluid samples. IVD includes various types of analytical tests and assays related to patient diagnosis and therapy that can be performed by analysis of a liquid sample taken from a patient's bodily fluids, or abscesses. These assays are typically conducted with automated clinical chemistry analyzers (analyzers) onto which fluid containers, such as tubes or vials containing patient samples have been loaded. The analyzer extracts a liquid sample from sample vessels and combines the sample with various reagents in special reaction cuvettes or tubes (referred to generally as reaction vessels). In some conventional systems, a modular approach is used for analyzers. A lab automation system can shuttle samples between one sample processing module (module) and another module. Modules may include one or more stations, including sample handling stations and testing stations (e.g., a unit that can specialize in certain types of assays or can otherwise provide testing services to the larger analyzer, which may include immunoassay (IA) and clinical chemistry (CC) stations.
An automation system for use with analyzers in an IVD environment moves tubes containing sample specimens between different stations within an analyzer or between analyzers. One common way to move these samples is by using passive carriers, such as pucks, along a friction track. Commonly, these automation tracks do not provide a large degree of precision when positioning samples. For example, passive pucks may be singulated and positioned mechanically using hard stops within the track. Singulation prongs may hold a puck in place once the puck has traversed the automation track to approximately the needed location. However, these prongs may not be adjustable for each puck and positioning a puck at a hard stop may not necessarily cause samples carried by the pucks to be repeatedly positioned relative to instruments, such as pipettes, along the automation track.
While hard stops may be used to position a puck with relative repeatability, devices which interact with the sample, such as pipettes, may require precise orientation and positioning of the sample at a given location on the track. The position and orientation of each sample may vary relative to the hard stops from puck to puck. For example, the manufacturing tolerances between two pucks may prevent a repeatable location of the bottom of the tube relative to a given singulation point. In addition, tubes may shift within the grasp of a puck, such as by tilting, or moving off center from a holding location within the puck as the puck traverses the automation or at the time an operator places the tube into the puck.
One common way to provide somewhat repeatable positioning of a sample tube relative to a surface of a puck engages a singulation point using a holder having self-centering springs. A self-centering spring mechanism can include three or more springs that provide horizontal forces relative to one another to engage the walls of a sample tube to hold the tube approximately in the center of the mechanism. Self-centering springs may be expensive to manufacture with the tolerances necessary to provide self-centering action. For example, in designs where self-centering springs include multiple springs that push relative to one another, the self-centering action requires the relative forces of the springs to be approximately equal. Furthermore, self-centering springs may only be designed to allow tubes with a relative range of sizes that may be narrower than desired. Self-centering springs may also be poorly suited for maintaining the position of a tube while undergoing large forces as the puck travels around an automation track. The springs may also be poorly suited for preventing a sample tube from tilting at insertion or while traversing an automation track. Accordingly, self-centering springs alone may be an expensive or inadequate solution to repeatably position a sample tube with respect to a known point on a track.